Laser printers described in Japanese Patent Application Publication Nos. HEI-11-133730 and 2005-37680 and also U.S. Pat. No. 6,751,428 are generally configured of a frame including a photosensitive drum, and a developing unit, commonly called a developer cartridge that is detachably mounted in the frame. The developer cartridge also includes a developing roller, and a case for accommodating developer. The case has an elongated shape that extends along the axial direction of the developing roller. The developing roller is positioned at a side surface of the case that extends along the axial direction of the developing roller. This type of laser printer also includes a pressing member for pressing the case so that the developing roller is pressed against the photosensitive drum in the frame, and a separating member for moving the case so that the developing roller separates from the photosensitive drum. This type of laser printer has been configured to apply both a pushing force with the pushing member for pushing the case of the developing unit and a separating force with the separating member for displacing the developing unit in a direction away from the photosensitive drum to single points on the case.
However, when these forces are applied to the same points on the developer case, it is necessary to reinforce the part of the case to which the force is applied and the vicinity thereof. To avoid this problem, U.S. Pat. No. 6,546,218 proposes a laser printer that divides the load so that the force of pushing the case with a pushing member and the force for separating the case with a separating member are not applied to the same point.
However, this type of load separating laser printer is configured so that the region near the longitudinal center of the developer case is pushed. Since there is potential for bending in the case with this construction, it is necessary to reinforce the laser printer by increasing the thickness of the case and the like.